Nickel-base dispersion hardened alloy



United States Patent 3,434,810 NICKEL-BASE DISPERSION HARDENED ALLOYWilliam J. Barnett, Brandywine Hundred, Del., assignor by mesneassignments, to Fansteel Inc., a corporation of New York No Drawing.Filed June 30, 1965, Ser. No. 468,592 Int. Cl. B22f 1/00, 9/00 US. Cl.29-182.5 6 Claims ABSTRACT OF THE DISCLOSURE Nickel-molybdenum alloys,which are modified with certain dispersed, particulate refractory oxidesand contain from 0.002 to 0.5 percent total carbon, are given improvedductility and high temperature strength properties by incorporatingtherein from 0.1 to 1.0 percent of zirconium or hafnium, of whichgreater than 0.02% is soluble in bromine-methanol solution.

in bromine-methanol solution, 0.002 to 0.5 percent total carbon, aboutfrom 1 to 6 percent by volume of a refractory oxide filler, said oxidehaving a free energy of formation at 1000 C. greater than 106kilocalories per gram atom of oxygen, the balance of the compositionsbeing nickel or a mixture of nickel with up to 40 percent of cobalt byweight, based on said nickel component, said oxide filler being in theform of particles in the size range of to 250 millimicrons, the averagebeing less than about 100 millimicrons, and said particles beingpervasively dispersed in the metal components of the alloys, the averageminimum diameter of the grains in said alloy being greater than 10microns. The invention is further particularly directed to the steps, ina process for making the novel alloys, comprising forming by powdermetallurgy a consolidated body having the chemical composition desired,and containing the refractory oxide dispersed in the nickel, cobalt ormolybdenum or in two or more of these components, cold-working saidconsolidated body at a temperature of up to 2000 F. to density itsubstantially to 100 percent density and to store energy thereinsufficient to permit recrystallization, and heat-treating saidcold-worked body by heating it to a temperature in the range of 1850 to2400 F.

In Alexander et al., US. Patent 3,180,727 there is described a novelsystem of alloys which are dispersionhardened and which are adapted foruse in high temperature applications such as in aircraft gas turbines.The alloys therein described have outstanding high temperatureproperties in that they retain their strengths well beyond thetemperature limits at which ordinary metals or alloys become unusable.In certain special applications, however, the problem is not so much theretention of strength at the highest temperatures, but rather this incombination with the adequate strength at the intermediate temperaturesfor use under very high stresses. Thus, in the manufacture of turbineblades, the base or root section of the turbine blade operates atsomewhat lower temperatures 3,434,810 Patented Mar. 25, 1969 than theair foil section but operates under higher stresses. In this and similarapplications the alloys heretofore described, even Whendispersion-modified, leave much to be desired.

There is, moreover, a need for a material which has an optimumrelationship between creep and rupture ductility. Materials ofconstruction lacking such ductility, such as cermets, may fail withoutwarning. On the other hand, materials having adequate rupture ductilitywill creep sufficiently that the imminence of failure can be detected bysuitable inspection during service life. Ideally, for use in a turbineblade assembly, an alloy should have a very low creep rate in the earlystages of its service life, but when failure is imminent it should havesufficient ductility that failure is not instantaneous and catastrophic.

Now, according to the present invention, it has been found that when thecomposition of certain dispersionhardened alloys is carefully controlledwithin specified, rather narrow limits, alloys can be produced whichhave adequate rupture ductility, i.e., greater than 2 percentelongation, and at the same time have a rupture strength, at 1400 F. andhours life, which is greater than 32,000 pounds p.s.i. It has been foundthat the molybdenum content of nickel or nickel-cobalt base alloysshould be carefully controlled within the limits of 12 to (22+8 timesthe wt. percent carbon) percent, and that such alloys should containsmall but critical amounts of carbon and zirconium or hafnium. The totalcarbon content of such alloys must be in the range from 0.002 to 0.5percent by weight. The zirconium or hafnium content should be from 0.1to 1.0, the alloys containing zirconium being a strongly preferredembodiment of the invention. The soluble zirconium or hafniumthat is,the amount soluble in bromine-methanol solution-should be greater than0.02 percent based on the total weight of the composition. Thecompositions must, of course, be dispersion-hardened by the presence ofabout 1 to 6 percent by volume of a very refractory metal oxide inparticulate form, the high degree of refractoriness of the oxide beingindicated by the fact that its free energy of formation at 1000 C. isgreater than 106 kilocalories per gram atom of oxygen in the oxide. Theaverage minimum diameter of the grains in the alloys is about from 10 to100 microns.

The major metallic component of the novel alloys is nickel, although thenickel may contain substantial but minor proportions of cobalt. Thus,the nickel may contain up to about 40 percent of its weight of cobalt,although normally the cobalt, if present, will be less than this amount.The molybdenum is a minor component but one which contributessubstantially to the strength of the alloys at intermediatetemperatures.

The carbon and zirconium or hafnium, although minor constituents, arecritically important in providing ductility and workability to thealloys. They also appear to contribute to the unusually high rupturestrengths at intermediate temperatures. Thus, an alloy containing 17.5percent molybdenum 'but without zirconium or carbon present, forinstance, and dispersion-strengthened with 2 percent thoria, might showa 1400 'F./ 100 hour rupture strength of say 28,000 p.s.i., whereas withboth carbon and zirconium present, as required according to thisinvention, such rupture strength is in excess of 32,000 p.s.i. It willbe understood that a combination of zirconium and hafnium can be used inthe alloy, provided the total proportion of these two elements is withinthe range given for either alone. The alloys containing zirconium aloneare greatly preferred.

Processes for dispersing refractory oxides such as thoria in matrixmetals such as nickel and nickel-molybdenum alloys are already wellknown in the art and are described, for instance, in Alexander et al.US. Patent 3,087,234. It is extremely important to have the refractoryoxide Well dispersed in the matrix metal. In describing the presentinvention, the oxide is said to be pervasively dispersed-that is, it isdispersed throughout the product, rather than being clustered togetherin a few areas at high concentration and being absent or substantiallyso in other areas. Moreover, the refractory oxide is present within thegrains as well as being observable at the grain boundaries.

In preparing dispersion-modified nickel and nickel alloys a preferredprocess is to precipitate the refractory oxide in particulate formtogether with the oxides of the matrix metals and then reduce the metalmatrix oxides to met-a1 by such methods as dry hydrogen reduction. It isimportant to effect complete reduction at this stage. The reduced powderis compacted to the form of a green billet, and this billet is thenconsolidated to a solid body which can serve as a starting material in aprocess of the present invention.

In a preferred embodiment of the invention, the starting material isprepared as a particulate solid comprising a compound of each metal ofthe group nickel and cobalt which is to be present in the final alloy,this solid having the refractory oxide dispersed in it; the particulatesolid is dispersed in an aqueous ammonium molybdate solution at a pH of5.5 to 8.5 whereby a molybdenum-containing coating is deposited on itssurface, the coated solid is separated from the solution and calcined at100 to 550 C., and the calcined product is heated at 450 to 1200 C. incontact with hydrogen, carbon, carbon monoxide or a hydrocarbon gas,whereby the particulate solid and its molybdenum-containing coating arereduced to their component metals and these metals are alloyed with eachother, the refractory metal oxides remaining unreduced and dispersedtherein.

The carbon and zirconium or hafnium in a process of the presentinvention are introduced into the powder of matrix metal containingthoria before such powder is consolidated. The carbon can advantageously'be introduced in its powdered elemental form. The zirconium or hafniumcan also be introduced as an elemental powder or it can be added aszirconium or hafnium hydride, a master alloy composition of zirconium orhafnium with a metal of the matrix, or a hydride of such master alloy.

It is important that the carbon, zirconium or zirconiumoontainingmaterial, or hafnium or hafnium-containing material, and the refractoryoxide-filled matrix metal be mixed together in the form of very finepowders. Thus, the particle size of zirconium or hafnium powderpreferably should be less than microns, the carbon particle sizepreferably should be minus about 200 mesh, and the refractoryoxide-filled molybdenum nickel matrix metal should preferably have asize less than 100 percent minus 200 mesh and 50 percent minus 325 mesh.In any event, the mixing should be extremely thorough, and the particlesize and mixing should be such as to elfect very intimate contactbetween the various components. Moreover, the mixing methods and thechoice of materials should be such as to provide uniform dispersion ofthe additives with respect to the matrix alloy.

Having prepared a powder blend containing the desired constituents, thepowder blend is compacted to a consolidated body having greater than 60percent density. This can be accomplished quite easily by hydrostaticcompaction. In this way a so-called green billet is obtained. In apreferred embodiment this billet is then sintered in hydrogen attemperatures below about 900 P. so as to remove any surface oxygen whichhas formed during the handling after the original reduction. Thisprecaution is taken to minimize the formation of zirconium oxide insubsequent steps of the process. The temperature is then increasedstepwise to about 1650 F. maintaining the dew point of the eflluent gasbeing used in the reduction at below 90 F. This sintering operation iscarried out in a can or within a protective environment. In aparticularly preferred embodiment the sintering is continued undervacuum at about 1650 'F. and a pressure less than 20 microns. After thishydrogen sinter under vacuum the billet is cooled to room temperatureand sealed under this vacuum. Alternatively, the billet can be cooledunder hydrogen or pure argon. In any event, oxygen contamination is tobe avoided.

The sintered billet is then extruded to consolidate it. The density isthereby increased to about 99 percent of theoretical.

If the extrusion operation leaves in sufficient residual stored energy,such as if the recrystallization temperature is less than about 2400 F.for two hours, the consolidated product is recrystallized. Otherwise theproduct is worked at temperatures below 2000 F. by swaging, forging,bar-rolling, etc. This results in a reduction of the recrystallizationtemperature to the range of 1850 to 2200 F. for alloys with less than 3percent thoria. With alloys containing more than 3 percent thoria therecrystallization temperature may remain above this figure. In a processof the invention the worked product is recrystallized at appropriatetemperature.

For compositions of this invention containing about .1 to .3 percentcarbon a further step may advantageously be employed consisting ofheating to approximately 2200 F. to cause any carbides present todissolve, and then quenching the system to retain the carbon insolution. The product thus obtained can advantageously then be aged at atemperature in the range of 1400 to 1800" F. for times from 4 to 24hours. It will be understood that this solution heat-treatment can becombined with the aforementioned final recrystallization step.

The novel compositions of the invention which can be prepared by theprocesses above described are particularly well adapted for use as amaterial of construction in any situation where retention of highstrength at intermediate temperatures-say 1000 to 1500 F.are encounteredin service. The products also have high utility at very hightemperaturessay 1800 F. and above. At 1800 to 1900 F. their strengthssurpass the so-called superalloys. Thus, they are well adapted for usein gas turbines where portions of the structure must have high strengthat very elevated temperatures and other portions must have good strengthat somewhat lower temperatures.

The invention will be better understood by reference to the followingillustrative examples:

EXAMPLE 1 A thoriated nickel-15 percent molybdenum alloy powder wasprepared by adsorbing molybdate on a nickel carbonate-thoriacoprecipitate, and reducing the resulting product with hydrogen. Thenickel carbonate-thoria coprecipitate was prepared using the techniqueof Example 5 of U.S. Patent 3,019,103 except that twice as much thoriawas used, and the thoria was introduced as Th(NO solution. Thecoprecipitate was filtered and washed, and then treated with a solutionof ammonium molybdate, whereupon molybdate adsorbed on the nickelcarbonate. The resulting product was filtered and dried at 400 C., andthen reduced with hydrogen by treating the dried mass for 2 hours at 400C., 2 hours at 650 C. and finally for 6 hours at 850 C.

The chemical composition of the thoriated nickelmolybdenum alloy powderwas, by weight percent: 1.84% T 14.98% Mo, 0.0028% C, less than 0.001%S. One hundred percent of the resultant powder would pass a 200 meshscreen.

Three tenths percent by weight of zirconium hydride and fiveone-hundredths percent by weight of Darco carbon, the average particlesize of each additive being less than ten microns, was cone-blended fortwo hours. A billet was prepared by hydrostatically compacting thepowder blend at 60,000 p.s.i. The billet was machined to a rightcircular cylinder and was welded into a mild steel can containingentrance and exit tubes for passing Stress rupture properties of samplescut from the annealed bar were:

Specimens from the swaged bar which were annealed at 1850 F. for 2 hoursplus 2200 F. for 2 hours yielded the following rupture properties:

Test Elongation, Reduction Temperature, Stress, p.s.i. Life, hrs.percent of Area,

13. percent Stress rupture strength of a specimen of the extruded barafter annealing at 2200 F. for 16 hours was:

Test Elongation, Reduction Temperature, Stress, p.s.i. Life, hrs.percent of Area, F. percent EXAMPLE 3 A thoriated nickel-18 percentmolybdenum alloy powder was prepared by the method described inExample 1. The chemical composition of the thoriated nickel-molybdenumalloy powder was, by weight percent: 1.91% ThO 17.58% Mo, 0.009% C,0.00l1% S. Thoria size as measured by X-ray techniques was 13millimicrons. One hundred percent of the resultant powder would pass a200 mesh screen. Three-tenths perment by weight of zirconium hydride andfive-tenths percent by weight of ground and sized -200/ +325 meshspectro-graphic stick carbon, the average particle size of the ZrHadditive being less than ten microns, was cone-blended for 2 hours.

From this powder a billet was prepared, canned, and reduced with dryhydrogen, all as described in Example 1, the reduction conditions beingas follows:

The billet was heated slowly to 490 F. under a flow of about 7 cubicfeet per hour of said hydrogen. After about 16 hours at temperature thedewpoint of the effluent hydrogen was less than '90 F. The temperaturewas then increased to 760 F. for 4 hours, then to 1000 F. for 2 hours,then to 1625 F. for 2 hours, the dewpoint of the effluent hydrogen aftereach heating period being below '90 F.

After the reduction was completed, hydrogen flow was terminated, and thecanned billet was evacuated at temperature. After about 1% hours attemperature under vacuum an ultimate pressure of about 8 microns wasattained. The canned billet was slowly cooled to room temperature undervacuum.

The exit and entrance tubes were then forge-welded shut. The cannedbillet was extruded at 1700 F. to a reduction ratio of 8/1. Afterextrusion the mild steel can was removed by pickling.

Chemical analysis of the extruded bar showed less than 0.001 weightpercent sulfur, and 0.456 weight percent carbon.

By digesting the extruded bar in a bromine-methanol solution andanalyzing the soluble fraction for zirconium it was found that over 34percent by weight of the zirconium added remained as zirconium alloyedin the nickel-molybdenum alloy matrix. The remaining approximately 66percent (approximately 0.16 weight percent of product) was in the formof ZrO Zr(CN) or similar compounds insoluble in the digestion medium.

The thoriated nickel-molybdenum alloy bar was then canned in stainlesssteel tubing of about & wall thickness, heated to 1500 F. for 2 hoursand swaged from 1500 F. with reheating after each pass, to a reductionof about 63.9 percent in cross-sectional area. After swaging thestainless steel can was removed by pickling.

The swaged bar was annealed at 2200" F. for 2 hours. Metallographicexamination of the annealed bar revealed a relatively uniform,fine-grained, recrystallized micro structure.

Stress rupture properties of samples cut from the annealed bar were:

Test Elongation, Reduction Temperature, Stress, p.s.i. Life, hrs.percent of Area,

F. percent Other specimens from the swaged bar were solution treated at2200 F. for 2 hours, quenched in water and aged at 1650 F. for 16 hours.Stress rupture properties of these solution treated and aged specimenswere:

Test Elongation, Reduction Temperature, Stress, p.s.i. Life, hrs.percent of Area, F. percent EXAMPLE 4 The Ni-Mo-Th0 powder of Example 2was used in this example. T hree-tenths percent by weight each ofzirconium hydride and ground and sized 200/+325 mesh spectrographicstick of carbon, the average particle size of the ZrH additive beingless than 10 microns was cone-blended with this starting powder for twohours.

From this powder a billet was prepared, canned and reduced with dryhydrogen, all as described in Example 1, the reduction conditions beingas follows:

The billet was heated slowly to about 440 F. under a flow of about 7cubic feet per hour of said hydrogen. After about 16 hours attemperature the dewpoint of the effiuent hydrogen was less than F. Thetemperature was then increased to about 800 F. for 3 hours, then to 1000F. for 2 hours, then to 1610 F. for 4 hours, the dewpoint of theeffluent hydrogen after each heating period being below 90 F.

After the reduction was completed, hydrogen flow was terminated, and thecanned billet was evacuated at temperature. After about 2 hours attemperature under vacuum an ultimate pressure of about 2 microns wasattained. The canned billet was cooled to room temperature under vacuum.

The exit and entrance tubes were forge-welded shut, and the cannedbillet was extruded at 1700 F. to a reduction ratio of 8/1. Afterextrusion the mild steel can was removed by pickling.

Chemical analysis of the extruded bar showed 16.6 weight percentmolybdenum, less than 0.001 weight percent sulfur, and 0.262 weightpercent carbon. By digesting the extruded bar in a bromine-methanolsolution and analyzing the soluble fraction for zirconium it was foundthat over about 19 percent by weight of the zirconium added remained aszirconium alloyed in the nickel-molybdenum alloy matrix. The remainingapproximately 81 percent (approximately 0.222 weight percent of product)was in the form of ZrO Zr(CN) or similar compounds insoluble in thedigestion medium.

The thoriated nickel-molybdenum alloy bar was then canned in stainlesssteel tubing of about wall thickness, heated to 1500 F. for 2 hours andswaged, with reheating after each pass, to a reduction of about 62.3percent in cross-sectional area. After swaging the stainless steel canwas removed by pickling.

The swaged bar was annealed at 2200 F. for 2 hours. Metallographicexamination of the annealed bar revealed a relatively uniform,fine-grained, recrystallized microstructure.

hydrogen over the billet and for evacuation. The canned billet wasevacuated at room temperature to a pressure of less than about 50microns and back-filled with pure dry (dew point less than 90 F.)hydrogen. The billet was heated slowly to 400 F. under a flow of about 7cubic feet per hour of said hydrogen. After about 2 hours at temperaturethe dew point of the effiuent hydrogen was less than 90 F. Thetemperature was then increased to 700 F. for about 2 hours, then to 900F. for 1 hour, then to 1650 F. for 2 hours, the dew point of theeiiluent hydrogen after each heating period being below 90 F.

After 2 hours at 1650 F., hydrogen flow was terminated, and the cannedbillet was evacuated at temperature. After about /1 hours at temperatureunder vacuum an ultimate pressure of about microns was attained. Thecanned billet after having been cooled to ambient temperature undervacuum exhibited a leak rate as indicated by pressure rise in the systemof less than 1 micron in 60 minutes. The exit and entrance tubes wereforgewelded shut. The canned billet was extruded at 1700 F. to areduction ratio of After extrusion, the mild steel can was removed bypickling.

Chemical analysis of the extruded bar showed 14.5 weight percentmolybdenum, less than 0.001 weight percent sulfur, and 0.025 weightpercent carbon. By digesting the extruded bar in a bromine-methanolsolution and analyzing the soluble fraction for zironium it was foundthat over about 48% by weight of the zirconium added remained aszirconium alloyed in the nickel-molybdenum alloy matrix. The remainingapproximately 52 percent (approximately 0.142 weight percent of product)was in the form of ZrO Zr(CN) or similar compounds insoluble in thedigestion medium.

The thoriated nickel-molybdenum alloy bar was then heated to 1500 F. andswaged, with reheating after each pass, to a reduction of about 60.9percent in cross-sectional area. The swaged bar was annealed at 1850 F.for 2 hours. Metallographic examination of the annealed bar revealed arelatively uniform, fine-grained, recrystallized microstructure.

Thoria particle size in the swaged bar was 18 m This was calculated fromsurface area after extraction of the thoria, as follows:

The metal component of a powder product of the invention is dissolved inan acid, or in bromine-methanol, leaving the filler oxide particles,which are recovered by coagulating, centrifuging, washing and drying.

The Br -CH 0H extraction procedure is as follows: Calculate the weightof metal for extraction required to give approximately 0.2 gm. ThOresidue. Thus, 10 gm. of a metal containing 2 percent ThO are required.For each 10 gram portion of metal, prepare 500 ml. of solutioncontaining 5.3 percent Br by volume in dry methanol. subdivide themetal. If dense, machine to chips. Add the metal slowly with stirring tothe Br -CH OH solution. Place the solution in a water bath, and coolduring the addition. (Temperature should be 35 C.) Avoid frothing causedby excessive gas evolution. After all the metal is added, remove thesolution from the water bath, and allow to stand 24 hours withoccasional stirring. Allow the residue to settle. Carefully decant theclear supernatant. Centrifuge the remaining residue. Wash and centrifugethe solid residue repeatedly with dry methanol until the supernatantliquor is colorless. Retain all decants and washings for 24 hours to seeif additional residue settles out. If so, repeat the centrifuging andwashing procedure so as to include this material with the originalresidue. If, during washing, the ThO residue begins to peptize, fioc thematerial by adding 2 to 3 drops of concentrated HNO then continuecentrifuging. Dry the final, washed residue and weigh.

The surface area of the recovered oxide from the abovedescribed processis then measured by the conventional BET method or its equivalent. (P.H. Emmett in Symposium on New Methods for Particle Size Determination inthe Subsieve Range, Philadelphia: ASTM, 1941, p. 95.) From this surfacearea measurement, the mean particle diameter, D, is calculated from theexpression: D=6000/fA where f is the absolute density of the filleroxide particles in grams per milliliter and A, is their surface area insquare meters per gram.

Stress rupture properties of samples cut from the annealed bar were:

A thoriated nickel-15 percent molybdenum alloy powder was prepared bythe technique of Example 1. The chemical composition of the thoriatednickel-molybdenum alloy powder was, by weight percent: 1.91% ThO 17.58%Mo, 0.009% C. 0.00l1% S. Thoria size as measured by X-ray techniques was13 millimicrons.

One hundred percent of the resultant powder would pass a 200 meshscreen. Three-tenths percent by weight of zirconium hydride and fiveone-hundredths percent by weight of Darco carbon, the average particlesize of each additive being less than 10 microns, was cone-blended withthis powder for two hours.

A billet was prepared, canned, and reduced with dry hydrogen, all asdescribed in Example 1, the reduction conditions being as follows:

The billet was heated slowly to 400 F. under a flow of about 7 cubicfeet per hour of said hydrogen. After about 15 hours at temperature thedew point of the efiiuent hydrogen was less than F. The temperature wasthen increased to 600 F. for 1 hour, to 800 F. for 3 hours, and to 1 650F. for 2 hours, the dew point of the effluent hydrogen after eachheating period being below 90 F.

After the reduction was completed, hydrogen flow was terminated, and thecanned billet was evacuated at temperature. After about hours attemperature under vacuum an ultimate pressure of about 20 microns wasattained.

The exit and entrance tubes were forge-welded shut. The canned billetwas extruded at 1800 F. to a reduction ratio of 8/ 1. After extrusionthe mild steel can was removed by pickling.

Chemical analysis of the extruded bar showed 17.8 weight percentmolybdenum, less than 0.001 weight percent sulfur, and 0.025 weightpercent carbon. By digesting the extruded bar in a bromine-methanolsolution and analyzing the soluble fraction it was found that about 50percent by weight of the zirconium added remained as zirconium alloyedin the nickel-molybdenum alloy matrix. The remaining approximately 50percent (approximately 0.12 weight percent of product) was in the formof ZrO Zr(CN) or similar compounds insoluble in the digestion medium.

The thoriated nickel-molybdenum alloy bar was then heated to 1500 F. for2 hours and swaged from 1500 F. with reheating after each pass, to areduction of about 62.9 percent in cross-sectional area.

The swaged bar was annealed at 1850 F. for 2 hours. Metallographicexamination of the annealed bar revealed a relatively uniform,fine-grained, recrystallized microstructure.

Stress rupture properties of samples cut from the annealed bar were:

Elongation, Reduction Test Tempeature, Stress, p.s.l. Life, hrs. percentof Area,

percent 1, 400 35, 400 57. 1 8. 0 8. 7 1, 400 33, 500 136. 0 4. 0 7. 9

Other specimens from the swaged bar were solutiontreated at 2200 F. for2 hours, quenched in water and aged at 1650 F. for 16 hours. Stressrupture properties of these solution-treated and aged specimens were:

A thoriated nickel-21 percent molybdenum alloy powder was prepared bythe chemical method described in Example 1 and ball-milled to '200 mesh.The chemical composition of the thoriated nickel-molybdenum alloy powderwas, by weight percent: 2.74% ThO 21.4% Mo, 0.0046% C, less than 0.001%S. Thoria size as measured by X-ray techniques was 12 millimicrons.

This powder was cone-blended with, by weight, 0.30% of zirconium hydrideand 0.05% Darco carbon, and a billet was prepared, canned, and reducedwith dry hydrogen, all as described in Example 1, the reductionconditions being as follows:

The billet was heated slowly to 480 F. under a flow of about 7 cubicfeet per hour of said hydrogen. After about 16 hours at temperature thedewpoint of the effluent hydrogen was less than --90 F. The temperaturewas then increased to 800 F. for 2%. hours, then to 1000 F. for 1 /2hours, then to 1650 F. for 2 hours, the dewpoint of the efiluenthydrogen being below 90 F. after each heating period.

After the reduction was completed hydrogen flow was terminated, and thecanned billet was evacuated at temperature. After about 2 hours anultimate pressure of about 8 microns was attained. The canned billet wascooled to room temperature under vacuum.

The exit and entrance tubes were then forge-welded shut. The cannedbillet was extruded at 1875 F. to a reduction ratio of 16/1. Afterextrusion the mild steel can was removed by pickling.

The thoriated nickel-molybdenum alloy bar was then canned in stainlesssteel tubing of about wall thickness, heated to 1800 F. for 1 hour andswaged from 1800 F. with reheating after each pass, to a reduction ofabout 47.5 percent in cross-sectional area. After swaging the stainlesssteel can was removed by pickling. Hardness of the swaged bar wasapproximately 517 DPH.

The swaged bar was annealed at 2200 F. for 2 hours. Hardness of theannealed bar was 383 Diamond Pyramid Hardness. Metallographicexamination of the annealed bar revealed a relatively uniform,tine-grained, recrystallized microstructure.

Stress rupture properties of samples cut from the annealed bar were:

Test Elongation, Reduction Temperature, Stress, p.s.l. Life, hrs.percent of Area, F. percent EXAMPLE 6 The Ni-Mo-ThO powder of Example 5was used in this example. This powder was cone-blended with zirconiumhydride and Darco carbon, and a billet was 7 prepared, canned, andreduced with dry hydrogen, all as described in Example 5, the reductionconditions being as follows:

The billet was heated slowly to about 425 F. under a flow of about 7cubic feet per hour of said hydrogen. After about 16 hours attemperature the dewpoint of the efiluent hydrogen was less than F. Thetemperature was then increased to about 670 F. for 2 hours, then to 870F. for 2 hours, then to 1615 F. for 3 hours, the dewpoint of theeflluent hydrogen being below -90 F. after each heating period.

After the reduction was completed, hydrogen flow was terminated, and thecanned billet was evacuated at temperature. After about 1 /2 hours attemperature under vacuum an ultimate pressure of about 5 microns wasattained. The canned billet was slowly cooled to room temperature undervacuum.

The exit and entrance tubes were then forge-welded shut. The cannedbillet was extruded at 1700 F. to a reduction ratio of 8/ 1.

The thoriated nickel-molybdenum alloy extruded bar was canned instainless steel tubing as in Example 5 and then heated to 1900 F. for 2hours and swaged from 1900 F. with reheating after each pass, to areduction of about 51.9 percent in cross-sectional area. Hardness of theswaged bar was approximately 508 DPH.

The swaged bar was annealed at 2200 F. for 16 hours. Hardness of theannealed bar was about 381 Diamond Pyramid Hardness. Metallographicexamination of the annealed bar revealed a relatively uniform,fine-grained microstructure.

Stress rupture properties of samples cut from the annealed bar were:

A second piece of the thoriated nickel-molybdenum alloy extruded bar wascanned in stainless steel tubing of about wall thickness, heated to 1800F. for 1 hour and swaged from 1800" F. with reheating after each pass,to a reduction of about 62.9 percent in cross-sectional area. Afterswaging the stainless steel can was removed by pickling. Hardness of theswaged bar was approximately 517 DPH.

The swaged bar was annealed at 2200 F. for 2 hours. Hardness of theannealed bar was 401 DPH. Metallographic examination of the annealed barrevealed a relatively uniform, fine-grained, recrystallizedmicrostructure.

Stress rupture properties of samples cut from the annealed bar were:

This example was like Example 1 except that 0.3 percent ZrH was added tothe Ni-Mo-Th0 starting powder. The billet was sintered for 3 hours at400 F., 1 hour at 600 F., 2 hours at 875 F. and finally 2 hours at 1650F. in hydrogen and then evacuated. The billet was extruded at 1700 at8:1 ratio, swaged 60 percent at 1500 1 1 and heat treated for 2 hours at1850 F. 1400 F. stress rupture properties were:

40,600 p.s.i. for 16 hours 35,400 psi. for 77 hours 33,000 p.s.i. for235 hours I claim:

1. A dispersion-modified alloy characterized by having a 1400 F./ 100hour rupture strength greater than 32,000 psi. and a rupture ductilitygreater than about 2 percent elongation, the composition consistingessentially of, by weight, about from 12 to (22+8 percent C.) percent ofmolybdenum, 0.1 to 1.0 percent of zirconium or hafnium, of which greaterthan 0.02 percent is soluble in bromine-methanol solution, 0.002 to 0.5percent total carbon, about from 1 to 6 percent by volume of arefractory oxide filler, said oxide having a free energy of formation at1000 C. greater than 106 kilocalories per gram atom of oxygen, thebalance of the composition being nickel or a mixture of nickel with upto 40 percent of cobalt by weight, based on said nickel component, saidoxide filler being in the form of particles in the size range of to 250millimicrons, the average being less than about 100 millimicrons, andsaid particles being pervasively dispersed in the metal components ofthe alloy, the

3. A composition of claim 1 in which the average particle size of thedispersed oxide filler is less than about millimicrons.

4. A composition of claim 1 in which the element of the group consistingof zirconium ad hafnium is zirconiurn.

5. A composition of claim 1 in which the molybdenum content is 21percent, the carbon content is 0.02 to 0.03, and the refractory oxide isthoria and is present in the amount 2.75 percent by weight.

6. A composition of claim 1 in which the total carbon content is aboutfrom 0.1 to 0.3 percent by weight.

References Cited UNITED STATES PATENTS 3,067,032 12/1962 Reed et a1.29182.5

3,074,152 1/1963 Huntress 29-182.5

3,087,234 4/1963 Alexander et a1, 29182.5

3,166,416 l/l965 Worn 29--l82.5

FOREIGN PATENTS 1,213,625 3/1966 Germany.

CARL D. QUARFORTH, Primary Examiner.

R. L. GRUDZIECKI, Assistant Examiner.

